What makes an animal large or small? Part of it may be due to climate change.
It may be that these are reactions to rapidly rising temperatures due to global climate change according to Professor Yoram Yom-Tov of Tel Aviv University, who has been measuring the evolving body sizes of birds and animals in areas where climate change is most extreme.

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Changes that the professor has identified are happening primarily in higher latitudes, where Prof. Yom-Tov has identified a pattern of birds getting smaller and mammals getting bigger. The change, he hypothesizes, is likely a strategy for survival. Prof. Yom-Tov, who has spent decades measuring and monitoring the body sizes of mammals and small birds, says that these changes have been happening more rapidly recently.

His most recent paper on the topic, focused on the declining body sizes of arctic foxes in Iceland, appeared in Global Change Biology.

Animal populations in a wide variety of geographical areas (such as birds in the UK, small mammals in the arctic, and most recently foxes, lynx and otters in cold Scandinavian regions)are adapting to a shift in rising temperatures. Where temperature changes are most radical, such as those at higher latitudes, Prof. Yom-Tov has measured the most radical changes of these animals’ body size over time.

In his most recent paper, Prof. Yom-Tov and his Tel Aviv University colleague Prof. Eli Geffen report that arctic foxes are being influenced by changing water currents in the oceans. These changes, likely a result of climate change, affects the foxes’ food supplies. Hydrologists may be unsure as to why the shifts in currents are happening, but the effect in foxes is evident: their bodies are changing along with the changing currents.

Scientists are finding changes in animals’ bodies across the whole animal kingdom. "Climate change is affecting migration patterns and the behavior and growth of birds, mammals, insects, flowers, you name it," says Prof. Yom-Tov.

Smaller bodies allow mammals, for example, to cope with warmer temperatures, since a smaller body size gives the body a proportionally increased surface area for the dissipation of heat, he says. While a larger body may show improved nutrition due to a warmer climate. Though it may not be clear exactly how animal life may adapt, change it will with a warmer climate. Studying animals in selected regions where climate change may be more severe, will give clues to future changes.

"These animals need to adapt themselves to changing temperatures." says Prof. Yom-Tov. "If they don’t adapt, their numbers may decline. If they do, their numbers remain stable or even increase."